Polymer blending system

ABSTRACT

A system for blending polymers and other chemicals in an aqueous liquid is provided. Static mixers and tubes, preferably in one or more tube bundles, provide a volume sufficient to allow a residence time in the system to hydrate a polymer. Static mixers may be integrated with a tube bundle. The system may be mounted on a portable base such as a trailer. The concentration of polymer and chemicals in water may be controlled by a controller. A variable speed electric pump may be utilized to precisely control the amount of polymers or other chemicals added to the aqueous liquid.

This application is a continuation of U.S. application Ser. No.15/413,699 filed Jan. 24, 2017 which is a divisional application of U.S.application Ser. No. 14/528,648 filed Oct. 10, 2014, which is acontinuation of U.S. application Ser. No. 13/216,329, filed Aug. 24,2011, which is a continuation in part of Ser. No. 12/952,373 filed Nov.23, 2010, all of which are incorporated herein.

BACKGROUND OF INVENTION

1. Field of the Invention

This invention is directed to method and apparatus for placingwater-soluble polymers and other chemicals into water to produce optimumproperties of the solution and to obtain data to facilitate the process.More particularly, a portable tube bundle containing static mixers foreffective blending without excessive shearing or damage to the polymerand chemical transport and storage apparatus with sensors and aprogrammable chemical delivery system are provided.

2. Description of Related Art

One purpose of a blending or mixing system as disclosed herein is toallow a water-soluble polymer and other chemicals to be blended from adispersion in oil into water or an aqueous liquid and to obtain maximumbenefits of the polymer. Such a device is commonly called a blendingsystem when used in conjunction with the fluids used in oil and gaswells. It may be used in any application where there is a need to mixpolymer or other chemicals in a continuous and a controlled manner. Toinsure the effective and even distribution of the polymer or otherchemicals into the water, the polymer must be wet by the water andthoroughly dispersed such that the polymer does not form clusters oraggregates, often called “fisheyes.” The polymer normally requiressufficient agitation and retention time as to allow the polymer chainsto unfold, causing the polymer solution to reach its maximum dispersion.With batch mixing, this retention time is accomplished by the use oftanks that have a large enough capacity to allow the mixture properretention time prior to use. Normally, this is performed through the useof two or more compartmented tanks that allow mixing to occur in one ormore tanks while the fluid that has already been mixed in the other tankor tanks is pumped. The size of the tanks used for this type of batchmixing is dependent on the rate that the fluid is being pumped from thesystem and the total mixing time required for the chemicals being used,but the tanks are expensive to transport and they form a largefootprint. One of the major limitations to batch mixing is thatconditions may change and a batch may not be needed for pumping into awell. This creates the problem of disposing of the mixed solution.

The amount of fluid used in many oil and gas well completion operationshas increased in size. In horizontal wells, higher pump rates generallymust be used to perform flow or circulation within the wellbore duringcompletion operations, such as drilling out plugs and removing solids.The polymers that are introduced into the fluid medium help not only totransport the particles but also to reduce the frictional pressure lossas fluid is pumped at higher rates through tubulars in the well bore. Itis important that the polymers and any other chemicals added to thefluid be introduced in a controlled operation. Preferably, thecomposition and properties of the fluid mixed and pumped should bemeasured and the data preserved, along with additional information onwater quality, temperature, viscosity, and density.

Injection rates used in hydraulic fracturing operations have alsoincreased in recent years. Polymer is added to the fluids to decreasefriction pressure drop as the fracturing fluid (called “slick water”) isinjected. Other types of polymers may be used to help suspend proppantin the fluid. In many cases the polymers being used do not havesufficient contact and mixing time prior to being pumped into thewellbore to completely hydrate, thereby limiting the effectiveness ofthe polymers. This may require overdosing of chemicals to achieve thedesired results.

In some cases larger tanks with recirculation pumps have beenincorporated into the completion and fracturing operations in an effortto improve the mixing and retention time of polymers. However, therecirculation pumps may lead to excessive shear of polymers, which canbreak the long chains of the polymers that are being mixed, resulting inlower effectiveness of the polymer solution.

U.S. Pat. No. 7,048,432 discloses a method and apparatus for hydrating apolymer for use in wells. The polymer solution is directed through ahousing containing rotating impellers. U.S. Pat. No. 4,828,034 disclosesmixing a polymer into an oil-based fluid to form an oil-based polymerconcentrate, then injecting the oil-based slurry into a water stream andpumping the mixture through a high-shear pump and a static mixer into afirst holding tank, then pumping the liquid through a second high-shearpump into a second holding tank. U.S. Pat. No. 4,336,345 disclosesformation of a polymer concentrate containing an inhibitor to hydration,then reversing the inhibitor reaction to allow full hydration of thepolymer.

What is needed is a blending system that overcomes the lack of retentiontime, excess shearing of the solution, the complexity of batch andcontinuous operations disclosed above and that can maintain a steadypump and mixing rate at an economical cost.

BRIEF SUMMARY OF THE INVENTION

The method and apparatus disclosed herein eliminate the need for batchmixing and multiple retention tanks for polymer mixing. In-line staticmixers agitate and mix polymer in water as it is being pumped throughthe system. The static mixers generate gentle agitation, allowing thepolymer to be thoroughly mixed in the aqueous solution without damagingthe polymer by excessive shearing. The invention also provides improvedretention or contact time between the aqueous solution and the polymerby providing stable flow of the solution through tubes. The tubes may bein a tube bundle. The system may operate with a programmed controlsystem for chemical injection, thereby reducing the number of personnelrequired to perform the mixing operation, may be portable for transportto well sites, and may record data indicating composition and propertiesof the fluids blended.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a sketch of an embodiment of apparatus for continuous in-linehydration of polymer and apparatus for sensing and recording data.

FIG. 2 is a drawing of a tube bundle in a case as disclosed herein.

FIG. 3 is an isometric view of tubes and static mixers in a tube bundle.

FIG. 4 is an isometric view of a portable blending system as disclosedherein.

FIG. 5 is a sketch of a second embodiment of apparatus for continuousin-line hydration of polymer and apparatus for sensing and recordingdata.

FIG. 6 is an isometric view of a second embodiment of a portableblending system as disclosed herein.

FIG. 7 is an isometric view of another embodiment of a portable blendingsystem as disclosed herein.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, blending system 10 may intake water or an aqueousliquid into pump 11, which pumps the liquid through water flow meter 18Ato connection 12, where a second liquid stream is added to the water.Connection 12 may contain sensors 12A, which may be used to measuretemperature, salinity, surfactant or other chemical composition and anyother variable that is relevant to the properties or effectiveness ofthe blended liquid. Sensors 12A are connected to controller 15. Pump 11is necessary only if water pressure is not sufficient. The liquid maythen go to static mixer 13 (as shown) or directly to tube bundle 14.Static mixers 13 and 16 may be arranged to receive liquid before orafter tube bundle 14. Line 16A carries the blended liquid to pump 17.Polymer or other chemical is added to the water stream at connection 12in the form of a concentrated suspension or solution in the secondliquid, normally oil. Flow meter 18A measures the rate of water flow andflow meter 18B measures the rate of oil flow. Both flow meters send asignal to controller 15. Metering valve 19 controls rate of flow of theoil stream according to a pre-programmed signal from controller 15 tosupply a desired concentration of chemical in the stream exitingconnection 12. Such controllers and valves are well known in industry.Solenoid valves such as manufactured by Sun Hydraulics, for example, maybe used as valve 19 to control fluid flow rate based on electricalcontrol signals that shift a spool or cartridge. Controller 15 may bemanually changed during use or respond to signals from a sensor.

System 10 requires very little energy to operate and may use pressure ofthe water source. Alternatively, pump 11 may be necessary. In-linemixing allows a higher range of flow rates to be used without reducingthe effectiveness of the polymer being mixed by applying excessive shearrate to the solution.

System 10 preferably uses a continuous length of pipe or tube that istightly compacted to reduce the size of the overall package (a “tubebundle”), such as illustrated in FIG. 2 and FIG. 3. Tube bundle 30 (FIG.3) includes straight tubes 32 that may be placed parallel and connectedwith curved ends 20. A selected number of straight tubes 32 may includea segment containing static mixer 35. Static mixer 35 may be joined in astraight tube by flange 34, by a weld or by any other method for joiningtubes. The length and diameter of the tubes allows sufficient contacttime to allow the aqueous solution to become properly hydrated. The tubebundle may incorporate inline static mixers positioned throughout thelength of the assembly to gently agitate the solution during pumping andto insure complete and thorough mixing of the solution. A suitablestatic mixer is a “Kenics” mixer available from Chemineer, Inc. of NorthAndover, Mass. The entire tube bundle may be enclosed in box 14 (FIG.2), which may have insulated walls.

The tube bundle may be positioned in vertical, horizontal or inclinedposition. The tubes and connectors may be made of ferrous or non-ferrousmaterial, including plastics or rubber hosing or any combination. Thetubes must have sufficient diameter and length to provide a properretention time. The tubes may have a diameter from 2 inches to 6 inchesand a total length from about 100 feet to whatever length is necessaryto achieve the needed retention time. The volume of tubes should besufficient to provide proper retention time of the liquid in system 10.A plurality of tube bundles may be used in the system. They may beconnected in series or in parallel. The combination of directionalchange in tube bundles, combined with the inline static mixers,generates effective and thorough agitation and mixing of the polymer inthe aqueous solution. The directional changes further reduce the amountof time required for mixing without damaging the polymer molecules. Inone embodiment the volume of tubes and static mixers is selected toallow a retention time of 20 minutes at a pump rate of 100 gallons perminute. This contact time is defined as from the time the aqueous liquidand polymer is introduced into connection 12 until the time the solutionleaves the system through outlet conduit 17A.

In a different embodiment using tube bundles, the system may beassembled as a mobile unit that is small and light-weight and that canbe transported on a trailer. A trailer such as shown in FIG. 4 may beused to transport tube bundles or, as shown in the figure, may be usedto transport portable polymer system 40, or both. Multiple tube bundlesmay be mounted on a trailer and connected in series or in parallel toprovide greater capacity. The bed of the trailer may be storage tank 41,which serves as a spill-containment vessel. Vessel 41 is preferablysized to contain the volume of liquid to be transported in system 40.Barrier 42 forms a leak-free spill structure that encloses liquid tanks43. It is a very important feature of the trailer that the trailer hasbuilt-in capacity in tank 41 to hold the contents of the tanks 43. Tanks43 may hold a suspension of polymer in oil, such as available inindustry from chemical suppliers, and other chemicals. Tanks 43 may bemade from polymer and require rods 44 to prevent excessive deformationwhen the tanks are full of liquid. Liquid may be pulled from tanks bypneumatic-operated piston pump 45. Hose and reel 46 can be used for airsupply to operate pumps 45. The polymer concentrate may be pumpedthrough a hose (not shown) to metering valve 19 (FIG. 1). Pumps 45 mayincorporate an inline air regulator to control the pressure between thepneumatic pump and metering valve 19. This allows constant pressure tobe supplied to the metering valve as the valve opens and closes due tochanges in the flow rate of the incoming liquid and provides greatflexibility for a wide range of pump rates without affecting the mixratios. In one embodiment, positive pressure chemical injection pump 45may have programmable logic from controller 15 that allows the injectionof the chemicals to be maintained at a constant ratio based on the inputor pump rate of the incoming aqueous liquid measured at flow meter 18and also allows pump 45 to respond to selected variables such astemperature, pressure, salt composition in water, and any othermeasurable quantity that may be selected to control chemical injectionrate. In another embodiment, the rate of chemical injection isprogrammed using valve 19 to control flow rate, which may respond toselected variables, such as temperature, pressure, salt composition inwater, and any other measurable quantity that may be selected to controlchemical injection rate. Tube bundles such as shown in FIG. 2 may,alternatively, be installed on the same trailer as tanks 43.

Referring to FIG. 1, downstream of the blending and data acquisitionsystem is normally high-pressure pump 17, which may have pressure gauge17A at the output of the pump. Data indicating pressure at this point ispreferably sent to controller 15, where it may be recorded and laterused to analyze the effects of blending operations on pressure at thewellhead as fluid is injected.

FIG. 5 illustrates a second embodiment of the blending system 10. Thesystem includes components similar to those in the embodiment of FIG. 1including liquid pump 11, flow meter 18A and connection 12 which mayinclude sensors 12A. A source 43 of polymer or other chemical in theform of a concentrated suspension or solution is connected via conduit47 to a variable speed electric pump 61. A check valve 62 is positionedin the flow line between source 43 and pump 61. Conduit 48 directs thepolymer or other chemical into connection 12 as in the embodiment ofFIG. 1. The mixture leaves connection 12 into for example, a mixer 13,tube bundle 14, mixer 16 and pump 17 which may include a pressure sensor17A. Various combinations and locations of the mixers and tube bundlemay be utilized. From pump 17 the mixture is directed to the well viaconduits 55, 56. A coriolis mass flow meter 54 may be utilized tomeasure the mass flow rate. Pressure and mass flow rate data is sent tothe controller 15 where it is stored and can be analyzed along withother information from sensors 12A and flow meter 18A.

The amount of fluid from source 43 can be precisely controlled byoperation of the variable speed electric pump 61. Flow meter 18 ameasures the rate of water flow and sends a signal to the control 15.In-line check valve 62 prevents water pressure and flow from enteringinto the chemical or oil injection conduit 48. Controller 15 calculatesthe chemical volume required to meet the programmed dosage volume or oilinjection volume. It sends a signal to the variable speed motor andcalculates the Hertz value for the motor rotation speed to match thedesired volumetric outputs. The motor sends a signal back to thecontroller to verify that motor rotation has reached the pre-setchemical dosage requirements.

FIG. 6 shows an embodiment of a portable system for the embodiment ofFIG. 5 that can be transported on a trailer. The portable systemincludes a trailer 60 having wheels 73 and adjustable ground supports 74to support the trailer when it is not being towed. Upper frame member 75leads to a goose neck type connector. As in the embodiment of FIG. 3,the bed of the trailer may include a storage tank 41 which serves as aspill-containment vessel. Tanks 43 for chemicals are supported on bed41. A variable speed electric pump 61 is mounted on the trailer bed andincludes an inlet conduit 63 and an outlet conduit 62 which delivers thechemical to a connector located within tube bundle housing 14.Electrical power for the pump 61 is provided by a diesel generator 65. Astorage tank 64 for diesel fuel is mounted on upper frame member 75. Aninlet 71 is provided delivering water to the connector within the bundlehousing 14 and an outlet 72 for the mixed fluids is located at asuitable location on the bundle housing 14. A bundle 30 such as shown inin FIG. 3. is positioned within bundle housing 14. Controller 15 andsensors 17A and 18A and meter 54 can be located on the structure at anyconvenient location. The trailer may be covered by a suitable enclosurenot show having door panels in the sides for easy access.

FIG. 7 illustrates yet another embodiment of the system arranged on atrailer 80. This embodiment is similar to that of FIG. 6. However in theembodiment of FIG. 7 the tube bundle 30 shown in FIG. 3 is located onthe lower part of the trailer below or in the spill containment vessel41, for example. This eliminates hydrostatic pressure from the upperposition which allows the water to freely flow through the tubes withoutassistance of additional pumps. Bundle 30 in this embodiment includes aplurality of straight pipe sections 85 connected together by elbowsections 20. The straight pipe sections and the elbows are generallylocated in a single plane that is parallel to the horizontal plane ofthe truck bed or vessel 41. The bundle 30 includes an inlet 82 andoutlet 81 for the fluid being treated as well as inlets for thechemical(s) being added to the fluid. The bundle 30 may also includestatic mixers 35 as shown in FIG. 3 and can be attached to the undersideof vessel 41 by any suitable means.

Although the present invention has been described with respect tospecific details, it is not intended that such details should beregarded as limitations on the scope of the invention, except to theextent that they are included in the accompanying claims. Modificationsto the invention may be made as might occur to one skilled in the fieldof the invention within the scope of the appended claims. Allembodiments contemplated hereunder that achieve the objects of theinvention have not been shown in complete detail. Other embodiments maybe developed without departing from the spirit of the invention or fromthe scope of the appended claims.

I claim:
 1. A system for blending polymers to form a polymer solution inwater, comprising: a first conduit for connection to a source of water,a water flow meter connected to the first conduit, a second conduit forconnection to a source of a polymer in oil suspension, a variable speedelectric pump connected to the second conduit; a connector for mixingthe water and the polymer in oil suspension, the connector having twoinlets, one inlet connected to the first conduit and a second inletconnected to the second conduit, and an outlet through which a mixtureof the water and the polymer in oil suspension is capable of exiting theconnector, a controller configured to receive a signal from the waterflow meter and is adapted to regulate the speed of the variable speedelectric pump in response to the signal received from the water flowmeter; and, a tube bundle connected to the connector, the tube bundleincluding a plurality of sections of tubes.
 2. The system of claim 1further comprising a static mixer connected to the outlet of theconnector.
 3. The system of claim 1 further comprising a pump connectedto the source of water.
 4. The system of claim 1 wherein a volume of thetube bundle is selected to provide a selected retention time of themixture of the water and the polymer in oil suspension as the mixture ofthe water and the polymer in oil suspension flows through the tubebundle at a selected flow rate.
 5. The system of claim 1 wherein thetube bundle is enclosed in a heat-insulated box.
 6. The system of claim1 further comprising a sensor for sending at least one of a temperaturesignal and a chemical composition signal to the controller.
 7. Thesystem of claim 1 further comprising a high-pressure pump having adischarge pressure sensor on an output of the high-pressure pump,wherein the discharge pressure sensor is configured to send a pressuresignal to the controller.
 8. The system of claim 7 further comprising amass flow meter connected to the output of the high-pressure pump. 9.The system of claim 1 further including a source of water connected tothe connector.
 10. The system of claim 1 further including a pluralityof static mixers located within the tube bundle.